1. Field of the Technology
The technology presented herein relates to an optical range-finding sensor that detects the distance to a range-finding object, an object detection device and a self-cleaning toilet seat that employ the optical range-finding sensor, and a method for manufacturing such an optical range-finding sensor.
2. Description of the Related Art
Optical range-finding sensors are known in which irradiation light is irradiated from a light-emitting element to a range-finding object, the position of light reflected by the range-finding object is detected by a position detecting light-receiving element, and the distance to the range-finding object is measured by a triangulation technique.
FIGS. 7A and 7B are diagrams conceptually illustrating the schematic structure and action of a conventional optical range-finding sensor FIG. 7A is a plan view, and FIG. 7B is a see-through side view.
FIG. 8 is a conceptual diagram for illustrating the concept of triangulation technique with a conventional optical range-finding sensor.
A conventional optical range-finding sensor 101 includes a light-emitting element 102 that emits irradiation light Ls, a light-emitting side lens 103 that collects the irradiation light Ls and irradiates the light to a range-finding object MO, a light-receiving side lens 105 that collects reflected light Lr that is the irradiation light Ls reflected by the range-finding object MO, a position detecting light-receiving element 104 (PSD: Position Sensitive Detector) that receives the collected reflected light Lr and detects the position of the range-finding object MO, and a control processing integrated circuit 107 that controls light emission of the light-emitting element 102 and processes detection currents I1 and I2 from the position detecting light-receiving element 104.
Irradiation light Ls is reflected by the range-finding object MO and turns into reflected light Lr. The reflected light Lr forms a light spot on the light-receiving face of the position detecting light-receiving element 104, and the light spot is detected in the form of detection currents I1 and I2 from the output terminals of the position detecting light-receiving element 104.
The conventional light-emitting element 102 is configured of a semiconductor light-emitting diode (LED: Light Emitting Diode). Because a semiconductor light-emitting diode radiates irradiation light Ls in all directions of the element, in order to irradiate a necessary amount of irradiation light Ls to the range-finding object MO, it is necessary to increase the amount of light emitted from the light-emitting element 102 (the amount of irradiation light Ls) to increase the efficacy of the light-emitting side lens 103.
Specifically, the focal distance and diameter of the light-emitting side lens 103 are made very large so as to collect irradiation light Ls emitted from the semiconductor light-emitting diode. In addition to increasing the diameter of the light-emitting side lens 103 such that the position detecting light-receiving element 104 obtains the amount of light necessary for range finding, it is necessary to increase the product obtained by multiplying the forward current of the semiconductor light-emitting diode when driven by pulses by light-emitting time.
Furthermore, as mentioned above, because a semiconductor light-emitting diode radiates irradiation light Ls in all directions of the element, it was impossible to incorporate the diode with the position detecting light-receiving element 104 and the control processing integrated circuit 107 in the same light-transmitting resin sealed package.
That is, a light-transmitting resin sealed package 109e in which the light-emitting element 102 is sealed with resin and a light-transmitting resin sealed package 109r in which the position detecting light-receiving element 104 and the control processing integrated circuit 107 are sealed with resin are formed separately, the light-transmitting resin sealed packages 109e and 109r are connected/combined with a light-shielding resin sealed package 109s formed of a light-shielding resin, and after that, the resultant is fitted to a sensor case 101c. 
FIG. 9 is a characteristic graph conceptually illustrating the state of detection output versus the distance to the range-finding object detected by the position detecting light-receiving element of the conventional optical range-finding sensor.
Reflected Light Lr forms a light spot on a different position on the position detecting light-receiving element 104 depending on the position of the range-finding object MO, changing the detection currents I1 and I2. For this reason, a configuration is employed in which the distance Dis from the optical range-finding sensor 101 to the range-finding object MO is detected by detecting a detection output Ps (see FIG. 9) that is defined by Detection output Ps=Detection current I1/(Detection current I1+Detection current I2).
Because the conventional position detecting light-receiving element 4 has a single light-receiving face (light-receiving region) and the resistance value of the light-receiving region is uniform, the detection output Ps is inversely proportional to the distance Dis, and so the correlation characteristic Cre exhibits an inversely proportional curve, which means it is difficult to measure the distance to the range-finding object MO with high accuracy.
FIG. 10 is a diagram for illustrating the occurrence of errors in range finding that are caused by the spread of light irradiated from the light-emitting element of the conventional optical range-finding sensor.
It is configured such that irradiation light Ls from the light-emitting element 102 (semiconductor light-emitting diode) is collected by the light-emitting side lens 103 to collimate the light, but because the semiconductor light-emitting diode is not a point light source, the irradiation light Ls spreads to some extent.
For example, if the range-finding object MO is outside on the side opposite to the position detecting light-receiving element 104 with respect to the sensor optical axis Lax that is defined by the light-emitting element 102 and the light-emitting side lens 103, the position of a light spot formed by the reflected light Lr reflected by the range-finding object MO that enters the position detecting light-receiving element 104 is detected as the position corresponding to a range-finding object MOi located at a distance Disi that is closer than the original distance Dis, causing a range finding error.
As described above, the conventional optical range-finding sensor 101 employs a semiconductor light-emitting diode as the light-emitting element 102. Because of this, the amount of irradiation light Ls in the direction of the range-finding object MO that is necessary for range finding is small. Accordingly, measures had to be taken to achieve the amount of light necessary for range finding, such as increasing the focal distance and diameter of the light-emitting side lens 103 as well as increasing the product obtained by multiplying the forward current of the semiconductor light-emitting diode when driven by pulses by light-emitting time.
Furthermore, it was also necessary to dispose a light-shielding resin sealed package 109s (light-shielding portion) for shielding the light-transmitting resin sealed package 109r in which the position detecting light-receiving element 104 was sealed from light emitted from the light-transmitting resin sealed package 109e in which the light-emitting element 102 was sealed, making it difficult to reduce the size of the optical range-finding sensor 101 (sensor case 101c).
When measuring the distance to a black range-finding object MO that is located at a distant position, the measuring accuracy lowers due to an insufficient amount of irradiation light Ls.
Optical range-finding sensors that employ a position detecting light-receiving element as disclosed in, for example, JP H9-318315A and JP S63-198817A are known.